In view of the continuously increasing need for inexpensive animal protein to feed the rapidly increasing population on earth, and also in view of the fact that the total amount of arable ground remains constant or even decreases, it is of great importance to be able to produce more meat from animals from a given amount of feedstuff. It is therefore necessary to improve the efficiency of the production of nutritious meat of pigs, poultry, cattle, horses, sheep, dogs and fish, by the use of growth promoting and feed efficiency agents as an additive to animal livestock feed. The term "livestock" will be used herein to refer to such animals grown for food.
Up to now, antibiotics with a narrow activity spectrum such as zinc bacitracin penicillin and streptomycin have been used on a large scale as growth stimulants. Antibiotics with a broad activity spectrum such as tetracycline, oxytetracycline and chloric tetracycline have also been so used. Usually such agents operate indirectly as growth promoters: first by slowing or even inhibiting the formation of certain germs in the gastrointestinal canal, thereby rendering usable for the production of meat that portion of the animal's feed intake otherwise necessary for keeping the germs alive; and second, by their preventive action against infectious diseases which would use a certain amount of energy.
The use of antibiotics as growth stimulants in animal feedstuff, however, may involve a certain amount of danger to human health. If such antibiotics are continuously given to animals in high doses, the meat from such animals may contain traces of the antibiotics, which could lead to development of a resistance to the antibiotic therapeutic effects in a person consuming such meat. The warnings of scientific authorities already have led to administrative restrictioms in using such agents as growth stimulants. Continuous use of antibiotics as growth stimulants in the feedstuff of animals and other livestock, that is, for non-therapeutic purposes, may be prohibited in the future.
Apart from such antibiotics, other kinds of compositions have been used as growth stimulants. Such ingredients include compounds with a pronounced antimicrobiological effect also used in human medicine, for instance furazolidone, also 3-(5-nitro-2-furfuryliden-amino)-oxazolidone-(2), described for example in Jucker et al., Wiener Tierarztliche Monatszeitschrift, 1960, magazine 2/3. pages 100 to 103; or sulfanilamides. described in Swiss Pat. No. 467,025. Furazolidone is C.sub.8 H.sub.7 N.sub.3 O.sub.5, also N-(5-Nitro-2-furfurylidene-3-amino)-2-oxazolidone. Furazolidone, however, has the disadvantage of having a relatively pronounced toxicity. The prophylactic use of sulfanilamides has now been forbidden.
More recently, an increasing number of chemotherapeutic agents with an antimicrobiological effect have been used as growth stimulants to be added to the feedstuff of livestock. These have been specifically developed for this purpose. Some examples are: 2-(2-chinoxalinyl methylene) hydrazine carbonic acid methyl ester-N1,N4-dioxide, known under the generic name "carbadox", and olaquindoc 2'-hydroxyethylcarbamoyl)-3-methylchinoxalin-di-N-oxide. Both compounds, however, exhibit a certain degree of toxicity, and are also suspected as possibly being carcinogens.
It has recently been proposed to use a compound with the generic name "nitrovine" as a growth stimulant and additive to livestock feed. This compound may be described as 1,5-bis-(5-nitro-2-furyl)-1,4-pentadien-3-on-amidinhydrazonehydrochloride; see Swiss Pat. No. 460,501 as well as Schneider et al.. Landwirtschaftliche Forschung, 1970, volume XXIII, magazine 4, pages 350 to 352.
It is also common practice to use, as growth stimulants in feedstuffs, antibiotics which are not used in human medicine, such as virginiamycin. Such compounds usually develop their effect by suppressing the intestinal flora, thereby avoiding their feed-consuming metabolism. At the same time, they prevent diarrhea, salmonella, colienteritides and similar problems resulting from infectious diseases, which lowers effective feed utilization.
If these newly developed chemotherapeutics are administered during the entire rearing period of livestock or other animals, some precautions must be observed. The meat from such animals contains traces of such ingredients which are hygienically doubtful, and cross-resistances may be built up. Residues of antimicrobial inhibitors may cause technological problems in the microbiological treatment of animal products. See Eichhoff, MERCK-Kontakte 3/74, page 34. Also, in a manner similar to the action of pesticides, a concentration or build-up of such toxic substances in the human body is possible in certain organs. It is therefore advisable to use such compounds only in very small doses.